1. Field of the Invention
The present invention relates to an etching solution composition for metal films for use in the manufacturing processes of liquid crystal display devices and semiconductor devices.
2. Description of Related Art
As the etching solution used in the manufacturing processes of liquid crystal display devices and semiconductor devices, a liquid mixture of fluorinated acid, nitric acid, acetic acid, and water; a liquid mixture of fluorinated acid, nitric acid, and water; a liquid mixture of fluorinated acid, ammonium fluoride, and water; a liquid mixture of hydrochloric acid and nitric acid; a liquid mixture of diammonium cerium nitrate (IV), nitric acid, and water; a liquid mixture of diammonium cerium nitrate (IV), perchloric acid, and water; a liquid mixture of phosphoric acid, nitric acid, acetic acid, and water; or a liquid mixture of phosphoric acid, nitric acid, and water is generally known.
Out of these, phosphoric acid based etching solutions are frequently used since they are stable and inexpensive, have little effect on an insulation film in the lower layer, and excel in the controllability of etching.
In the field where multi-layer wiring is required such as the field of liquid crystal display devices and semiconductor devices, a significant challenge in the future would be the control to configure the section of the wiring to be a tapered shape to keep up with the trend of the utilization of thinner films in more layers.
From the growing need of lower resistance for wiring materials in accordance with the advancement of the densification and miniaturization of patterns, aluminum or an aluminum alloy, for example, is being used as the wiring material; typical multi-layer wiring is fabricated by forming an insulation layer on aluminum or aluminum alloy wiring by any suitable means, followed by further forming aluminum or aluminum alloy wiring in the upper layer thereon. The aluminum or aluminum alloy wiring in the lower layer needs to have a cross section of a tapered shape to improve the covering property of the insulation layer lying thereon. In this case, the control of the tapered shape of the wiring in the lower layer (the control of side etching) is important, and failing to obtain a tapered shape with a desired angle may lead to breaks of the wiring in the upper layer.
It is possible, in a wet etching process, to form wiring with a tapered shape by etching an aluminum or aluminum alloy film using a liquid mixture of phosphoric acid-nitric acid-acetic acid-water. It has been reported that, in using the liquid mixture of phosphoric acid-nitric acid-acetic acid-water of volume ratio of 16:2 to 8:2:1, when the baking temperature of the resist is adequate and the resist adheres adequately to the metal film, etching will occur with a large taper angle close to a right angle; however, when the baking temperature of the resist is slightly lower than an adequate temperature, the etching solution tends to penetrate into the interface between the resist and the metal film, thereby causing the etching surface of the metal film to be formed in an one-step tapered shape inclining toward the center of the metal film, and when the concentration of nitric acid is raised, the taper angle will be decreased (see, for example, patent document 1 listed below). On the other hand, it is known that when the concentration of nitric acid is low, an one-step tapered shape with a large taper angle will be formed, but when the concentration of nitric acid is further raised, the etching rate at the interface between the resist and metal film will be increased thereby resulting in the formation of a two-step tapered shape consisting of a step with a small taper angle formed on the side of the interface between the resist and metal film and a step with a large taper angle formed on the side of the substrate, and when the concentration of nitric acid is further raised, an one-step tapered shape with a small inclination will be formed (see, for example, patent document 2, patent document 3 and literature 1 listed below). However, a higher concentration of nitric acid will increase the etching rate of the aluminum or aluminum alloy film and therefore degrade the controllability of the etching, making it difficult to obtain a desired definite tapered shape.
Further, based on the fact that a larger area of aluminum exposed from the resist film will result in a higher etching rate, a technique has been disclosed in which, in order to obtain a desired definite taper angle, for example, in the range of 30 to 50 degrees, the shape of the wiring is formed by a dry etching, thereafter a resist pattern is further formed to remove the resist in the end portion of the wiring, which is to be formed into a tapered shape, and the area adjacent thereto where there is no wiring, and thereafter aluminum film is etched using an etching solution consisting of phosphoric acid, nitric acid, acetic acid, and water (an optimal nitric acid composition is 11.36% to 12.78% by mass)(see, for example, patent document 4 listed below). However, this method, which requires both of a dry etching process used for forming the wiring and a wet etching process used for forming the tapered shape of the end face of wiring, is cumbersome.
On the other hand, it has been reported that when the nitric acid concentration is high in the etching solution consisting of phosphoric acid, nitric acid, acetic acid, and water, the resist will degrade causing cracks on its surface; however, the cracks will be confined within the resist surface (see, for example, patent document 2 listed below). It also has been reported that the resist will be protected by adding acetic acid (see, for example, literature 1 listed below). However, it has been confirmed from an electron micrograph observation of the resist surface for the case in which nitric acid concentration is high that not only cracks are produced on the resist surface, but also etching traces due to the exudation of the etching solution (hereinbelow referred to as “etching solution exudation trace”) will occur further inside the etching surface at the interface between the resist and a metal film. As the result of the etching solution exudation trace, the metal film surface will lose its smoothness by being etched, which will cause a problem since a desired shape can not be obtained. Currently, there is no prior art disclosed on the method of preventing the “etching solution exudation trace”, and no technique has been developed for etching free from causing etching solution exudation trace when the nitric acid concentration is high.
Furthermore, as the miniaturization of semiconductor processes proceeds, there is a growing need of a high quality metal film surface having a high level of smoothness and no surface roughness after etching. As an attempt to improve the state of the metal film surface after etching by adding an additive, an etching solution has been proposed which is principally composed of phosphoric acid, nitric acid, acetic acid, and water and further added with a trialkylamine oxide surfactant for the purpose of preventing the adsorption of hydrogen which is produced when the metal film is etched by nitric acid onto the metal film surface, since the adsorption of bubbles onto the metal film surface will inhibit etching thereby impairing the smoothness of the etching surface (see, for example, patent document 5 listed below). Moreover, it is known that it is effective to add a surfactant for the purpose of enhancing the wettability to improve the microprocessing capability of the etching solution (see, for example, patent document 6 listed below); however, there has been no mention on forming a tapered shape having a high quality etching surface having a high level of smoothness and no surface roughness.
As described so far, there has not been developed an etching solution composition which can form a tapered shape with a high quality etching surface having a high level of smoothness, a small taper angle, and no surface roughness, and will not cause etching solution exudation trace.